The invention relates to non-rising stem valves in which the stem passes out of the valve housing through a bonnet having a packing gland. Sometimes when such valves are in service, open and under pressure the stem packing must be changed while the valve remains open.
Although the invention is not limited to inclusion in gate valves, it was developed for use with a gate valve of the sort shown in these prior U.S. Pat. Nos.:
Crain et al., 3,349,789, Oct. 31, 1967 PA1 McGee, 3,789,875, Feb. 5, 1974 PA1 Boitnott, 3,990,679, Nov. 9, 1976